Chlamydia is one of the most widespread bacterial sexually transmitted diseases in the world causing an estimated 92 million infections per year with over 2.8 million infections in America alone. Chlamydia trachomatis can cause pelvic inflammatory disease, ectopic pregnancy and infertility in women and is a co- factor in HIV transmission. The ocular form of Chlamydia has visually impaired over 8 million people and is the leading cause of preventable blindness. With treatment programs failing to stem the disease spread in North America, a vaccine is widely acknowledged as the only way by which to prevent the suffering caused by Chlamydia and a goal that the National Institute of Allergy and Infectious Diseases (NIAID) has been pursuing. Previous attempts to create an effective vaccine have proven unsuccessful;in part because Chlamydia is an intracellular pathogen that requires cell mediated immunity. The discovery described in this proposal makes substantial progress towards a Chlamydia vaccine by uniquely surmounting the technical challenges of stimulating T cell immunity. Inspired by the global magnitude of need for a Chlamydia vaccine and propelled by recent advances in proteomic technology, genomics and knowledge of Chlamydia immunology, we have identified novel antigens critical to the design of an effective C. trachomatis vaccine. The Chlamydia genome has been fully resolved, due to support from the NIAID, and the proteins from which protective T cell antigens are derived have been inferred. Chlamydia biologists now know the correlate for protective immunity to C. trachomatis is T cell interferon gamma production. In addition, excellent murine models exist to evaluate Chlamydia vaccines. We have assembled a team and developed a comprehensive strategy to identify novel T cell antigens and evaluate them in murine models of infection based on a detailed understanding of dendritic cell immunobiology. We believe that we have achieved a breakthrough by using immunoproteomics to identify T cell antigens that are expressed in Chlamydia infected dendritic cells - achieved in part because we have access to the latest generation of mass spectrometry capable of detecting peptides at the subfemtomolar level. Using mass spectrometry, the first specific aim of this study is to discover the identity of additional Chlamydia peptides eluted from MHC class I and class II molecules expressed on the surface of Chlamydia infected dendritic cells. Our second specific aim is to uncover the immunological significance of Chlamydia MHC binding peptides. Based on the antigens we know, and others we plan to uncover in this study, this grant outlines our proposed research to induce cell mediated immunity in animal models, a major step in the development of a safe and effective Chlamydia vaccine for humans. Funding for this project will accelerate progress toward a Chlamydia vaccine, which will be a major medical achievement for global health. PUBLIC HEALTH RELEVANCE: Often asymptomatic, sexually transmitted Chlamydia trachomatis infects over 92 million people per year globally and is a leading cause of pelvic inflammatory disease (PID) that results in 2-3 million annual cases of infertility and is linked to 60,000 maternal deaths per year due to ectopic pregnancy. With control programs failing, the development of a safe and effective Chlamydia vaccine would represent a fundamental breakthrough in global health as well as saving in excess of $13.5 billion per year world wide in treatment costs. In this proposal a novel immunoproteomic approach is described based on identifying Chlamydia peptides capable of producing protective cellular immunity that shows great promise towards the development of a Chlamydia vaccine.